In recent years, as higher levels of properties are required of semiconductor elements, their environment of usage also becomes increasingly severe. Therefore, Si (hereinafter referred to as an Si semiconductor element) which has conventionally been used as a semiconductor element material is being replaced by SiC, GaAs, GaN and the like. These are hereinafter referred to as an SiC semiconductor element, a GaAs semiconductor element and a GaN semiconductor element, respectively. Each of the SiC, GaAs and GaN semiconductor elements has excellent properties including an excellent pressure resistance, an achieved increase in operation temperature and an enlarged band gap, and is applied to power transistors and optical devices such as LEDs. These semiconductor elements are called next-generation semiconductors and are required to operate at high temperatures and hence solder joints used therefor may also reach a temperature of about 250 to 280° C. Accordingly, a high-temperature solder for use in such next-generation semiconductors is needed.
Furthermore, in general, a semiconductor element may be connected to a heat sink such as a metal core or a ceramic sheet for heat dissipation and a high-temperature solder is also used for such connection purposes.
Some high-temperature solders have heretofore already been known and an Au-20Sn solder alloy which is an Au—Sn eutectic composition alloy is known as such a conventional high-temperature lead-free solder alloy. The Au-20Sn solder alloy has a eutectic temperature of 250° C. and can be hence used at 250° C. or more but less than 280° C. However, it is a very expensive material.
Exemplary low-cost, high-temperature lead-free solder alloys include an Sn—Sb based solder alloy, a Bi based solder alloy, a Zn based solder alloy and an Ag-containing sintered alloy. Of these, an Sn—Sb based solder alloy is more excellent than a Bi based solder alloy, a Zn based solder alloy and an Ag-containing sintered alloy in terms of thermal conductivity, corrosion resistance and joint strength.
Each of Patent Literatures 1 to 3 discloses an Sn—Sb—Ag—Cu solder alloy obtained by adding Ag and Cu to an Sn—Sb solder alloy, as a high-temperature adder alloy which can also be used in a temperature range of 250 to 280° C.
In other words, each of Patent Literatures 1 to 3 discloses an Sn—Sb—Ag—Cu solder alloy having a solidus temperature in excess of 250° C. in order to improve the heat resistance.
In addition, Patent Literature 4 proposes a solder alloy obtained by adding Fe to an Sn—Sb—Ag—Cu solder alloy in order to improve the heat cycle properties.